This application is a 35 USC 371 application of PCT/DE 00/01975 filed on Jun. 23, 2000.
The invention relates to a common rail injection system for injection of fuel into an internal combustion engine, in particular a large-scale diesel engine, having an injector housing, which communicates via a fuel inlet with a central high-pressure reservoir. The reservoir is supplied with fuel from a fuel tank via a high-pressure pump, and the fuel, as a function of the position of a 3/2-way magnet valve integrated with the injector housing passes from the high-pressure reservoir into a high-pressure bore of an injection nozzle that is integrated with the injector housing and includes a nozzle needle. The nozzle needle is axially displaceable counter to the prestressing force of a nozzle spring that is received in a nozzle spring chamber, and the 3/2-way magnet valve has a control piston, which can be moved back and forth between a closed and an open valve position and which on one of its two ends is coupled with an armature and whose other end projects into a chamber which is maintained at substantially atmospheric pressure. In the open valve position, the fuel inlet communicates with the high-pressure bore of the injection nozzle, and in the closed valve position, the fuel inlet is closed by the control piston and the high-pressure bore of the injection nozzle communicates with a fuel outlet and with the chamber which is maintained at substantially atmospheric pressure. One such injector is known from German Patent Disclosure DE 43 41 543.
In common rail injection systems, a high-pressure pump pumps the fuel into the central high-pressure reservoir, which is called a common rail. From the high-pressure reservoir, high-pressure lines lead to the various injectors that are assigned to the engine cylinders. The injectors are triggered individually by the engine electronics. The rail pressure is applied to the 3/2-way magnet valve, which keeps the high-pressure bores to the conventional injection nozzle pressureless. Not until the magnet receives electric current does the 3/2-way magnet valve open the communication between the rail and the injection nozzle, and the fuel reaches the combustion chamber, bypassing the nozzle needle that is lifted counter to the force of a valve spring. Accordingly, the onset and end of injection are determined by the onset and end of a delivery of electrical current to the magnet. The duration of this delivery of current is definitive for the injection quantity.
Upon switching of the 3/2-way magnet valve, the control piston moves back and forth between the closed and the open valve position. The phase in which the control piston is located between the open and the closed valve position is called the flight phase. In experiments performed in the context of the present invention using conventional injectors, at high injection pressures of about 1500 bar in the flight phase, instabilities in the motion of the control piston have been demonstrated. These instabilities have occurred particularly whenever, at a constant rpm, the supply of current to the magnet was varied. As a result of these instabilities, the engine might no longer function correctly in the affected range.
An object of the invention is to optimize the motion of the control piston in the flight phase.
The invention includes a common rail injector for injection of fuel into an internal combustion engine, in particular a large-scale diesel engine, having an injector housing. The central high pressure reservoir communicates via a fuel inlet with a central high-pressure reservoir, which is supplied with fuel from a fuel tank via a high-pressure pump, the fuel, as a function of the position of a 3/2-way magnet valve integrated with the injector housing passes from the high-pressure reservoir into a high-pressure bore of an injection nozzle that is integrated with the injector housing and includes a nozzle needle. The nozzle needle is axially displaceable counter to the prestressing force of a nozzle spring that is received in a nozzle spring chamber. The 3/2-way magnet valve has a control piston, which can be moved back and forth between a closed and an open valve position and which on one of its two ends is coupled with an armature and whose other end projects into a chamber which is maintained at substantially atmospheric pressure. In the open valve position the fuel inlet communicates with the high-pressure bore of the injection nozzle, and in the closed valve position, the fuel inlet is closed by the control piston and the high-pressure bore of the injection nozzle communicates with a fuel outlet and with the chamber which is maintained at substantially atmospheric pressure. The invention is attained in that a first throttle restriction is disposed between the high-pressure bore and the fuel outlet. As a result, the function of the 3/2-way magnet valve becomes independent of the diversion pulse. With the throttle, the overflow quantity upon switching can be controlled.
One special type of embodiment of the invention is characterized in that a second throttle restriction is disposed between the fuel outlet and the chamber which is maintained at substantially atmospheric pressure. The second throttle restriction prevents fuel, acted upon by pressure, from reaching this chamber in the flight phase. The inflow of pressurized fuel into the this chamber could otherwise lead to pressure pulses on the end face of the control piston. These pressure pulses would counteract the valve spring force and could lead to an impairment in the function of the 3/2-way magnet valve.
A further special type of embodiment of the invention is characterized in that a sleeve for guiding the control piston is inserted into the injector housing. The sleeve can be built into the injector housing either with or without the control piston already mounted. The use of the sleeve has the advantage that in production the sleeve can be machined much more simply than the injector housing. Furthermore, a worn sleeve can easily be replaced with a new sleeve. There is no longer any need to replace the injector housing.
A further particular type of embodiment of the invention is characterized in that one opening each is disposed in the sleeve in the region of the fuel inlet, the fuel outlet and the communication with the high-pressure bore, and each opening discharges into a respective annular chamber. This assures good distribution of the fuel.
A further particular type of embodiment of the invention is characterized in that the sleeve is formed of a high-speed steel having a greater hardness than the injector housing. This markedly increases the service life of the injector.
Still another particular type of embodiment of the invention is characterized in that the diameter play at the throttle restrictions amounts to from 0.005 to 0.05 mm. In experiments performed in the context of the present invention, these values have proved to be especially advantageous.